---
title: types
sidebarTitle: types
---

# `fastmcp.utilities.types`


Common types used across FastMCP.

## Functions

### `get_cached_typeadapter` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L41" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
get_cached_typeadapter(cls: T) -> TypeAdapter[T]
```


TypeAdapters are heavy objects, and in an application context we'd typically
create them once in a global scope and reuse them as often as possible.
However, this isn't feasible for user-generated functions. Instead, we use a
cache to minimize the cost of creating them as much as possible.


### `issubclass_safe` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L116" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
issubclass_safe(cls: type, base: type) -> bool
```


Check if cls is a subclass of base, even if cls is a type variable.


### `is_class_member_of_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L126" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
is_class_member_of_type(cls: Any, base: type) -> bool
```


Check if cls is a member of base, even if cls is a type variable.

Base can be a type, a UnionType, or an Annotated type. Generic types are not
considered members (e.g. T is not a member of list\[T]).


### `find_kwarg_by_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L148" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
find_kwarg_by_type(fn: Callable, kwarg_type: type) -> str | None
```


Find the name of the kwarg that is of type kwarg_type.

Includes union types that contain the kwarg_type, as well as Annotated types.


### `replace_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L377" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
replace_type(type_, type_map: dict[type, type])
```


Given a (possibly generic, nested, or otherwise complex) type, replaces all
instances of old_type with new_type.

This is useful for transforming types when creating tools.

**Args:**
- `type_`: The type to replace instances of old_type with new_type.
- `old_type`: The type to replace.
- `new_type`: The type to replace old_type with.

Examples:
```python
>>> replace_type(list[int | bool], {int: str})
list[str | bool]

>>> replace_type(list[list[int]], {int: str})
list[list[str]]
```


## Classes

### `FastMCPBaseModel` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L34" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Base model for FastMCP models.


### `Image` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L174" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Helper class for returning images from tools.


**Methods:**

#### `to_image_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L211" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
to_image_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.ImageContent
```

Convert to MCP ImageContent.


### `Audio` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L233" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Helper class for returning audio from tools.


**Methods:**

#### `to_audio_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L270" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
to_audio_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.AudioContent
```

### `File` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L291" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Helper class for returning audio from tools.


**Methods:**

#### `to_resource_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L330" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python
to_resource_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.EmbeddedResource
```

### `ContextSamplingFallbackProtocol` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L414" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
